Technical Field
The present invention relates to power systems, and more particularly to Wide-area Measurement System (WAMS) based control of Grid-Scale Storage (GSS) for power system stability enhancement.
Description of the Related Art
Deregulation of the electricity market has pushed the power transmission grid to its transfer limit. The increasing penetration of renewable energy resources is stressing the power grid with great uncertainties due to their high degree of intermittency. As a result, a power grid is more likely to experience transient frequency fluctuation and oscillations, which may lead to system instability or even cascading failure and blackout.
Traditionally, a Power System Stabilizer (PSS) is used to enhance power system angular stability by providing supplemental damping to the oscillation of synchronous machine rotors through the generator excitation. The damping is provided by an electric torque applied to the rotor which is in phase with the speed variation. PSS helps extend the transfer capability of a tie-line in a power system so that the thermal limit of the tie-line can be reached. The supplemental control provided by PSS is very beneficial during line outages and large power transfers between areas.
However, PSS suffers from a number of limitations/drawbacks. For example, one such limitation/drawback is that under certain circumstances, PSS can provide negative damping on the rotor which leads to power system instability.
Another such limitation/drawback is that PSS parameters are usually designed offline based on a linearized model of the non-linear power system with the assumption that the oscillation modes do not change under different grid operating conditions. This design philosophy often degrades the performance of PSS when a power system experiences a large change or the power system behaves in a more non-linear way under large disturbances. This limitation becomes more obvious with the increasing penetration of renewable energy resources.
Yet another such limitation/drawback is that PSS is designed to damp a particular critical oscillation mode. When multiple oscillation modes appear due to changes in system operating conditions, PSS becomes less effective.
Still another such limitation/drawback is that PSS uses only local information for damping control and is thus most effective for damping local oscillations while its effectiveness in damping inter-area mode oscillations is limited.